Novak Conversions Jeep Wrangler YJ engine mounts

Swapping my 4.2 block for a 4.0 block

Dougie87

Dougie87

New Member
Joined
Apr 8, 2024
Messages
5
Location
South Carolina
Ok, I'm at a crossroad of changing my 4.2 block over to the 4.0. I did a 4.0 head swap on my 4.2, and I found out from the shop, that I may be leaking oil from the back of the block. I have not gotten it home to break it down and see yet. My question is, I have the 4.0 head, intake and exhaust from the swap, will the 4.0 replace ok if I get the bell housing to mate up my AX15 tranny? I'm looking at short blocks right now but wondered if someone out there has done this. I know I will like the extra horsepower.
 
Dougie87 said:
Wasn't planning on it. My head conversion was with a 2150. I would like to have evidence, but cost is a factor.
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The block isn't what gives the extra horsepower...the EFI and tuning is what does that. You're probably better off just fixing the oil leak if that's an option.
 
Dougie87 said:
Ok, I'm at a crossroad of changing my 4.2 block over to the 4.0. I did a 4.0 head swap on my 4.2, and I found out from the shop, that I may be leaking oil from the back of the block. I have not gotten it home to break it down and see yet. My question is, I have the 4.0 head, intake and exhaust from the swap, will the 4.0 replace ok if I get the bell housing to mate up my AX15 tranny? I'm looking at short blocks right now but wondered if someone out there has done this. I know I will like the extra horsepower.
Click to expand...

Chris said:
I'm going to tag @NovakConversions since they'll know for sure.
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I appreciate the confidence but we don't actually get into the 4.2 or 4.0 much at all aside from maybe converting to a different transmission. I'm not much help on this one. Sorry guys.

-Dustin
 
Dougie87 said:
That's what I think too, we'll find out when I can get to it. Thanks for the feedback, that's the course I'll probably take.
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also check the valve cover gasket. I had a cork gasket in mine when I bought it and that leaked within a year. The leak looked like a RMS. Use one of the good rubbery steel fel pro or victor reinz ones if you can.
 
Novak Conversions Jeep Wrangler YJ engine mounts
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